Electrostatic emulsion development



Dec. 1962 R. w. GUNDLACH ELECTROSTATIC EMULSIQN DEVELOPMENT Filed Feb. 6, 1961 INVENTOR. ROBERT W. GUN DLACH ATTORNEY United States Patent Oilfice 3,058,115 Patented Dec. 11, 1952 3,368,115 ELECTRGS'EATIQ ElviULSltlN DEVELOPP/EENT Robert W. Gundlach, Victor, N.Y., assignor to Xerox Corporation, a corporation of New York Filed Fan. 6, 19rd, Ser. No. 87,403 Claims. (Cl. 117-37) This invention relates to xerography and in particular to improved methods and apparatus for Xerograpnic development.

1n the art of xerography it is conventional to form an electrostatic latent image on a xerographic plate including a photoconductive insulating layer and to develop the latent image on the xerographic plate by the selective electrostatic attraction thereto of suitable finely divided particles. Some development techniques, known to the art and in commercial use, share the common characteristic that the particles are maintained and applied in a dry condition and involve the use of finely divided electrostatically charged powder materials either by themselves or in conjunction with other particles and either as a flowing body of particles, as a film of particles on a surface, or as a gaseous suspension of particles. There is, however, another form of xerographic development, known as liquid immersion development, in which development is effected by immersing a latent image bearing member in a dispersion of finely divided particles suspended in a volatile insulating liquid. This development method is particularly attractive for many applications, since it involves only relatively simple apparatus and since it has proven capable of developing images of extremely high resolution and with a minimum of apparent graininess. However, this method, in common with the previously described dry powder methods, requires a supply of fine pigmented particles having very carefully controlled properties. For good results in development, the particles must be of highly uniform and carefully controlled particle size, and such size control is difiicult to accomplish with extremely fine particles as are required. Furthermore, the particles are generally required to have a carefully controlled electrostatic charge which is acquired by triboelectrification or similar processes. This in turn requires careful control of the chemical composition and structural uniformity of the developer particles. These problems are not insoluble, and suitable developer powder materials for xerography are commercially available but their manufacture remains a relatively expensive and difficult process. As a further point, developer powders, by their inherent nature, do not adhere strongly or permanently to the latent image bearing member or other common surfaces such as paper. It therefore becomes necessary with any of the above-described xerographic development methods, to use special materials or techniques to secure permanent images in which the developer particles are tightly and permanently bonded to a support surface.

It is pertinent to note that there are also known processes for developing electrostatic images in which a developer in the form of a liquid ink is sprayed or atomized in air toward the image bearing surface and deposits thereon. Such methods eliminate the problems associated with image permanency and with the need for predispersed developer materials but share in other known disadvantages associated with xerographic development methods involving the use of gaseous suspensions of developer particles.

Now in accordance with the present invention, there are provided novel methods and ap aratus whereby a suspension of liquid developer droplets is formed in an insulating carrier liquid directly at the time and place of utilization thereof and whe eby the droplets are charged to an optional and controllable electrical polarity.

It is accordingly the principal object of the invention to provide improved methods and apparatus for liquid immersion development.

It is a further ob ect of the invention to provide improved methods and apparatus for xerograpnic development in which a developer liquid is electrostatically dispersed in a carrier liquid and attracted to the surface to be developed.

it is a further object of the invention to provide methods and apparatus in which a supply of developer liquid is repeatedly dispersed in a carrier liquid, reagglomerated and redispersed for xerographic development.

These and further objects will become apparent in the course of the following specification and claims taken with the drawings, wherein:

FIG. 1 represents a partially schematic isometric view of one form of xerographic development apparatus according to the invention;

FiG. 2 represents a partially schematic isometric View of a second form of development apparatus according to the present invention; and,

FlG. 3 represents a partially schematic isometric view of a third form of development apparatus according to the present invention.

Generally a xerographic development process starts with an electrostatic latent image pattern on a suitable surface. The most common method of forming such an image involves depositing a uniform electrostatic charge on a xerographic plate including a photoconductive insulating layer and then selectively discharging the uniform charge by exposure of the plate to a pattern of light and shadow. Other methods are also known for forming electrostatic latent images on xerographic plates. Furthermore, methods are also known and are in use for forming charge patterns on insulating materials which do not have photoconductive properties. In general, any electrostatic latent image or electric field pattern, regardless of how formed, is a suitable starting point for development in accordance with the present invention.

Xerographic plates fall generally into one of two classes. The first class of plate comprises a layer of vitreous photoconductive insulating material such as vitreous selenium, sulfur or the like which may optionally be coated on any suitable support material. The second class includes a photoconductive insulating layer comprising a dispersion of photoconductive particles, such as zinc oxide, in an insulating binder material such as a resin. The photoconductive insulating layer may again be coated on a suitable support material. The first class of plate is characterized as having a photoconductive insulating layer which is substantially impermeable to liquids whereas the second class of plates have photoconductive insulating layers which physically resemble highly pigmented paints and accordingly tend to be slightly permeable or absorbent toward liquids. Both classes of plates are suit ble for use with the present invention, but the results achieved are slightly different as will be further described hereinafter. Similarly, latent image bearing surfaces of the non-photo conductor type may be divided into permeable and impermeable types of m terials. The fi st class is comprised of such things as insulating plastic films which may be selfsupporting or coated on various supports such as paper or metal Webs, and the second class is composed of pe meable materials such as carefully dried naner. A ain. these classes of latent ima e bearing materials are both us ble with the methods of the present invention, although again with somewhat var ing results.

In liquid development processes enerally. development is accomplished by immersin or otherwise contactin the xerographic plate or other latent image bearin member with a liquid developer material comprising a suspension of finely divided developer material in a liquid carrier. The carrier liquid must be a highly insulating material with a volume resistivity of at least about ohm centimeters in order to avoid discharge of the electrostatic latent image, and should not be a solvent for any part of the xerographic plate or other latent image bearing member. Additionally, it should not be excessively viscous in order that it not prevent the motion of the developer material under the influence of electric fields and should be at least moderately volatile, since the desired result of the development process is a dry image. This is most readily achieved by allowing the carrier liquid to evaporate from the developed image leaving only the developer material behind. Many different liquids are suitable for use as carrier liquids in liquid development generally and more specifically in connection with the present invention. A particularly useful class of materials comprises refined petroleum hydrocarbons having a volatility at least about as great as that of kerosene and preferably not more than about that of gasoline. Such materials are widely available and variously known as min ral spirits, petroleum naphtha, Stoddard solvent, etc., and are also sold under such trade names as Solvesso (Esso Standard Oil Company) and Sovasol (Socony Mobil Oil Company). A particularly useful material of this class is Sohio Odorless Solvent (SOS) sold by the Standard Oil Company of Ohio. Suitable liquids other than petroleum hydrocarbons are known including carbon tetrachloride and these may also be employed. For general information on liquid development processes priOr to the present invention, reference may be had to British Patent 755,486, US. Patent 2,899,335, and US. Patent 2,913,353.

Turning now to FIG. 1, there is, in partially schematic form, a representation of one form of apparatus suitable for use with the present invention. The apparatus includes a container 10 which is filled with an electrically insulating carrier liquid 11 of the type already described and is capable of receiving within liquid 11 at Xerographic plate 12 or other electrostatic latent image bearing member. Xerographic plate 12 is shown for illustrative purposes only as comprising a photoconductive insulating layer 13 on a conductive support layer 14 and is also shown for illustrative purposes only as supported within containers 10 by an electrical lead 25. It will be understood that in a commercial form of apparatus other support means for plate 12 may be provided, including frames, guides, easels and the like. Positioned adjacent to container 10 is a second container 16 which contains a supply of developing liquid 17. In accordance with the present inventon, developing liquid 17' 'is a liquid material which is substantially immiscible with the carrier liquid 11 and is capable of liquid 11 in the form of very small veloper material may also optionally contain a soluble dye or the like in order to render the developer material visible and therefore to make the developed images likewise visible. Since the developer material is employed in being dispersed in droplets. The dethe form of a dispersion within the insulating carrier liquid 11, it cannot discharge the electrostatic latent image until it deposits thereon and therefore the requirements for the electrical resistivity of the developer material are much less stringent than for the carrier liquid. In the course of development the developer material deposits on the electrostatic latent image in the form of discrete and mutually separated droplets or particles. As development proceeds, these .droplets may coalesce to form a thin film which might, if conductive, tend to discharge the latent image. At this point, however, the latent image is already substantially developed, and furthermore, a thin film is much less effective in discharging a surface than is a bulk mass of material such as the carrier liquid. For these reasons, the developer material may have a resistivity many orders of magnitude less than that of the carrier liquid which must generally have a resistivity at least on the order of about 10 ohm centimeters. As

will become apparent from a further description of the present invention, developing liquid 17 not only need not have the high electrical resistivity of carrier liquid 11 but must, in fact, have a substantially lower resistivity in order to operate effectively. In accordance with the present invention, an almost limitless number of materials exist which meet the above requirements for developing liquid17 and which may be used in conjunction with the present invention. One suitable class of material cornprises aqueous inks such as ordinary commercial fountain pen inks. In some cases it may be desirable to add a few percent of alcohol to such inks to reduce their surface tension. Another particularly useful class of materials includes glycols, preferably including soluble dyes. Particularly suitable examples include ethylene glycol containing about 5% of crystal violet or malachite green dye.

One end of a tube 18 is immersed in liquid 17 and leads from container 16 into container 10 and terminates in a finely drawn capillary nozzle 19 which is pointed toward xerographic plate 12 and spaced on the order of a few inches therefrom. At least the portion of tube 18 which is immersed in liquid 11 should be of an insulating. material such as glass. A high voltage DC. power supply 29 is connected by lead 24 to electrode 21 which is immersed in liquid 17 and by lead 25 to xerographic plate 12 which is also supported in container 10 and liquid 11 Y thereby. Some forms of xerographic plate do not include an electrically conductive support layer 14. In such cases the plate may be temporarily supported on a conductive plate attached to power supply 20, or power supply 20 may simply be connected to container 10 if the container is electrically conductive. Similarly, the power supply may be connected directly to container 16 instead of to an immersed electrode 21 where the container 16 is itself electrically conductive or may be connected to an electrode within tube 18. Power supply 20 is adapted to apply a high direct current potential on the order of 4000 volts between liquid 17 and xerographic plate 12. When the power supply is energized, liquid 17 within tube 18 and capillary tip 19 is electrified by virtue of the conductivity of liquid 17 and tiny droplets of liquid 17 are drawn from capillary nozzle 19 and are attracted toward the xerographic plate. Functionally, the developer liquid should generally be sufiiciently conductive to create a conductive path therethrough to electrify nozzle 19 from electrode 21. These emitted droplets carry an electrostatic charge which is determined by the connection made to power supply 20. If the negative terminal of the power supply is connected to electrode 21, then the droplets will be negatively charged; whereas, if the positive terminal is connected to the electrode 21, the droplets will be positively charged. In accordance with conventional xerographic practice, the droplets polarity is selected on the basis of the polarity of the electrostatic latent image on the xerographic plate and on whether it is desired to develop the charged or uncharged portion of the electrostatic latent image.

After issuing from the capillary tip 19, the droplets travel toward the Xerographic plate and are electrostatically attracted to the charged or uncharged area of the plate, depending upon their polarity and that of the plate. Some of the graphic plate but may instead, assuming they are heavier than liquid 11, settle out at the bottom of container 10 forming a layer of liquid 17. This, however, is not in any way detrimental to the functioning of the apparatus. If the droplets are lighter than liquid 11, they will, of course, form a layer at the top of liquid 11. There is also shown in FIG. 1 a development electrode 15 in the form of a fine mesh screen which is positioned very closely adjacent to the electro-static latent image on plate 12 and is electrically connected theretothrough lead 26. Such an electrode is not an essential feature of the invention but is included to illustrate advantages inherent in the invention. Such an electrode, as is known droplets may not reach the xeroin the xerographic art, is useful for drawing out the electrostatic line of force from xerographic plate 12 thereby securing better development of continuous tone type images and other images including large solid areas. Various forms of development electrodes, as used with prior art development, tend to become clogged or dirtied by the developer material employed and have required frequent cleaning. In accordance with the present invention, however, electrode 15 may intercept some of the droplets of developer liquid 17, but these droplets Will simply coalesce to form a thin liquid film on the electrode which will simply drain oft to the bottom as illustrated, or top, as the case may be, of liquid 11. Accordingly, no cleaning of this electrode is required. After a sufficient amount of developer liquid 17 collects in container 1%. it may be withdrawn for reuse through drain valve 2-2. Alternatively, liquid 17 may be returned to container 16 by a pump 23. If desired, a float switch (not shown) may be included in container ill to automatically actuate pump 23 when sufficient developer liquid 17 accumulates in container is. The apparatus of FIG. 1 then becomes completely automatic, and it is only necessary to replenish the supply of developer liquid 17 in the container 16 from time to time. As obvious to one skilled in the art, the above apparatus may readily be modified to function with liquids 17 which float on liquid 11.

Thus, in carrying out development according to the present invention, a xerographic plate or other electrostatic latent image bearing member is immersed in container 10, and power supply 2%) is energized to cause droplets of liquid developer material to be dispersed within the carrier liquid in container 10 and to be selectively deposited on the electrostatic latent image. This deposition is generally complete in a short time on the order of a few seconds to a minute. The Xerographic plate is then removed from container 10 carrying with it a visible pattern of developer liquid in image configuration. Where the xerographic plate or other latent image bearing member is of the permeable type previously described, the developer material is not only attracted to the plate but is absorbed within the plate within a few seconds to form a completely permanent image which needs no further fixing operation to be rendered permanent. if the xerographic plate is of the impermeable type, the developed image will remain on the plate surface rather than soaking in. This will lead to the formation of a dry and moderately adherent image if the developer material is itself volatile. If, however, a non-volatile material such as ethylene glycol is employed, the image will remain in the liquid condition. if, however, the xerographic plate is then pressed against a sheet of paper or other pe meable transfer material, the developer material will transfer from the impermeable plate to the permeable transfer material and soak into the transfer material forming an inherently permanent image thereon. Again, the need for a separate fixing operation or special transfer material has been eliminated and the xerogra hic plate can be washed free of any remaining developer material and be reused.

FIG. 2 shows another form of apparatus according to the invention. In this embodiment container 16 and tube 18 are combined into a single structure and tube 18 passes through the wall of container 10 rather than passing thereover. It is obvious, however, that elements 16 and 18 are the complete functional equivalents of the corresponding elements in FIG. 1. Also included in this embodiment is an electrically conductive ring 3% which is positioned adjacent and in front of capillary nozzle 19 and which is electrically connected, by lead 27 to the terminal of high voltage power supply 20 opposite to that connected to electrode 21. When the power supply is energized, there is thus established an electric field between capillary nozzle 1% and ring 3%; which causes droplets of developer liquid 17 to issue from capillary nozzle 19 and pass through ring 3% toward xerographic plate 12. in this embodiment the electric field causing droplet emission is entirely independent of any electrostatic charge pattern on xerographic plate 12, and there is thus provided a more complete control over droplet emission than is provided by the arrangement of HG. l.

in both FIGS. 1 and 2 the liquid levels in containers and 16 are depicted as being approximately equal. This is representative of a typical, but not a necessary, operating condition. in general, the two liquid levels will vary from each other by an amount depending on such factors the interfacial tension and relative densities of liquids and 17. The general requirement is that the hydrostatic pressure of liquid 17 within capi.- lary nozzle should approximate the pressure in liquid 11 adj' cent to nozzle 19. if the pressure inside nozzle It? one s the outside pressure by more than an amount 2/: depends upon the size of the capillary nozzle and the interface tension of the two liquids, liquid 17 will dribble out of nozzle l even in the absence of an electric field. och dribbling, if slight, is tolerable because be reclaimed and reused, and because the liquid 1? ca formation of one droplets still takes place in the usual manner when power supply is energized. if, however, the pressure inside capillary nozzle 19 is excessively smaller than the pressure outside, liquid 11 will tend to displace liquid within the nozzle and this condition must be avoided since it tends to inhibit the desired function of the apparatus when power supply 24) is energized.

T e invention has heretofore been illustrated in terms Oil separate containers for the difierent liquids employed and in terms of a xerographic plate vertically positioned for development. Neither of these conditions is necessary, and FIG. 3 illustrates another form of apparatus according to the invention in which these features are absent. in this embodiment, xerographic plate 12 is positioned in container beneath the surface of liquid 11 with its photoconductive layer 13 facing downward. Developer liquid 1'7 is maintained within container 10 in the form of a discrete layer at the bottom thereof. Tube 18 communicates with liquid 17 and ends in an upwardly pointing capillary nozzle 19 which i located within liquid 11 and preferably just above the interface between liquid 11 and liquid 17. Electrode 21 is positioned within liquid 17 and preferably close to or even within tube 18. Upon energization of power supply 2% as through switch 9 droplets of liquid 17 are projected into liquid 11 from nozzle 19 and are electrostatically attracted upward toward xerographic plate 12;, thereby developing the elec rostatic image on plate 12 in the same manner as shown in connection with H68. 1 and 2. Any droplets which are not actually used for development purposes simply fall back to the layer of developing liquid 17. There is thus provided in this embodiment a recirculation of liquid 17 without the need for pumps or other accessory apparatus.

While the invention has been illustrated in terms of a single capillary nozzle 19, it is apparent that mulitple nozzles may also be employed. Also, the invention has been illustrated in terms of manual operation and of a stationary sheet-like xerographic plate. It will be apparent, however, that the invention is readily adaptable to various forms of xerographic plates or other latent image bearing members including those in the form of flexible webs or rotating cylinders. For example, a plate in the shape of a cylinder can be made to rotate to form a wall in the developing chamber of FIGS. 1 and 2 or can be rotated above and into contact with the surface with the developer bath in FIG. 3. These and other various other modifications as will be apparent to those skilled in the art lie within the scope of the invention and are intended to be encompassed by the appended claims.

What is claimed is:

1. The method of developing an electrostatic latent image bearing member capable of retaining electrostatic charges comprising contacting the member with a body of dielectric liquid, electrostatically generating within said dielectric liquid a supply of finely divided droplets of a developing liquid substantially immiscible with said dielectric liquid, and selectively electrostatically attracting said droplets through said body of liquid to said latent image bearing member in accordance with the latent image thereon.

2. The method of developing an electrostatic latent image on a latent image bearing member with liquid droplets comprising immersing the latent image bearing member in a first liquid having a volume electrical resistivity substantially suificient to prevent dissipation of said latent image, immersing in said first liquid an electrically insulating capillary nozzle filled with a second colored liquid substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, and establishing an electric field from said nozzle whereby said second liquid is caused to issue from said nozzle in the form of fine. droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said droplets.

3. The method of developing an electrostatic latent image on a latent image bearing member with liquid droplets comprising immersing the latent image bearing member in a first liquid having a volume electrical resistivity of at least about 10 ohm centimeters to prevent dissipation of said latent image, immersing in said first liquid an electrically insulating capillary nozzle filled with a second colored liquid substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, and establishing an electric field from said nozzle whereby said second liquid is caused to issue from said nozzle in the form of fine droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said drop-lets.

4. The method of developing an electrostatic latent image on a latent image bearing member with liquid droplets comprising immersing the latent image bearing member in a first liquid having a volume electrical resistivity substantially suificient to prevent dissipation of said latent image, immersing in said first liquid an electrically insulating capillary nozzle filled with a second colored liquid substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, and establishing an electric potential difference between said nozzle and said image bearing member whereby said second liquid is caused to issue from said nozzle in the form of fine droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said droplets.

5. The method according to claim 4 in which the potential difference is about 4,030 volts.

6. The method of developing an electrostatic latent image on a latent image bearing member with liquid droplets comprising immersing the latent image bearing member in a first liquid having a volume electrical resistivity substantially sufficient to prevent dissipation of said latent image, immersing in said first liquid an electrically insulating capillary nozzle filled with a second colored liquid substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, and establishing an electric potential difference between said nozzle and a ring electrode substantially encircling said nozzle whereby said second liquid is caused to issue from said nozzle in the form of fine droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said droplets.

7. The method of claim 6 in which the potential difference is about 4,000 volts.

8. The method of developing an electrostatic latent image on a latent image bearing member with liquid droplets comprising immersing the latent image bearing member in a first liquid having a volume electrical resistivity of at least about 10 ohm centimeters to prevent dissipation of said latent image, immersing in said first liquid an electrically insulating capillary nozzle filled with a colored ethylene glycol liquid substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, and establishing an electric field from said nozzle whereby said second liquid is caused to issue from said nozzle in the form of fine droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said droplets.

9. The method of developing an electrostatic latent image on a latent image bearing member with liquid droplets comprising immersing the latent image bearing memher in a first liquid having a volume electrical resistivity of at least about 10 ohm centimeters to prevent dissipation of said latent image, immersing insaid first liquid an electrically insulating capilliary nozzle filled with an aqueous ink substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, and establishing an electric field from said nozzle whereby said second liquid is caused to issue from said nozzle in the form of fine droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said dropletss 10. The method of developing and fixing an electrostatic latent image on a liquid permeable latent image bearing member with liquid droplets comprising immersing the latent image bearing member in a first liquid having a volume electrical resistivity substantially sufiicient' to prevent dissipation of said latent image, immersing in said first liquid an electrically insulating capillary nozzle filled with a second colored liquid substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, establishing an electric field from said nozzle whereby said second liquid is caused to issue from said nozzle in. the form of fine droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said droplets, removing the latent image bearing member from the first liquid and allowing the droplets of the second liquid to absorb into said latent image bearing member.

11. The method of developing and fixing an electrostatic latent image on a liquid impermeable latent image bearing member with liquid droplets comprising immersing the latent image bearing member in a first liquid having a volume electrical resistivity substantially sufficient to prevent dissipation of said latent image, immersing in said first liquid an electrically insulating capillary nozzle filled with a second colored liquid substantially immiscible with said first liquid and having a substantially lower electrical resistivity than said first liquid and substantially oriented toward said image bearing member, establishing an electric field from said nozzle whereby said second liquid is caused to issue from said nozzle in the form of fine droplets which are attracted to said image bearing member, the electrical polarity of said nozzle being identical with the desired polarity of said droplets removing the latent image bearing member from the first liquid, contacting the latent image bearing member with a sheet of liquid permeable material, and separating the permeable sheet from the image bearing member.

12. Apparatus for developing an electrostatic latent image on an image bearing member comprising container means having therein a body of dielectric liquid and adapted to receive an image bearing member within said dielectric liquid and having therein a supply of colored developing liquid having an electrical resistivity substantially less than that of said dielectric liquid and being substantially immiscible therewith, means to support an image bearing member within said dielectric liquid, a conduit filled with said developing liquid connecting said developing liquid with said dielectric liquid and terminating in at least one electrically insulating capillary nozzle within said dielectric liquid and substantially directed at said image bearing member, and means to establish at said capillary nozzle an electric field whereby said developing liquid is atomized from said nozzle into said dielectric liquid and is attracted toward said image bearing member.

13. Apparatus according to claim 12 in which said container means comprises a single container.

14. Apparatus for developing an electrostatic latent image on an image bearing member comprising a container having therein a body of dielectric liquid and adapted to receive an image bearing member within said dielectric liquid, means to support an image bearing member within said dielectric liquid, a container having therein a supply of colored developing liquid having an electrical resistivity substantially less than that of said dielectric liquid and being substantially immiscible therewith, a conduit filled with said developing liquid connecting said developing liquid with said dielectric liquid and terminating 10 in at least one electrically insulating capillary nozzle withsaid dielectric liquid and substantially directed at said image bearing member, and a high voltage DC. power supply electrically connected to the liquid within said capillary nozzle whereby said developing liquid is atomized.

15. Apparatus for developing an electrostatic latent image comprising a container having therein a body of dielectric liquid and adapted to receive an image bearing member within said dielectric liquid, means to support an image bearing member within said dielectric liquid, 9. container having therein a supply of colored developing liquid having an electrical resistivity substantially less than that of said dielectric liquid, a conduit filled with said developing liquid connecting said developing liquid with said dielectric liquid and terminating in at least one electrically insulating capillary nozzle within said dielectric liquid and susbtantially directed at said image hearing member, a substantially ring-shaped electrode substantially encircling said capillary nozzle, and a high voltage direct current power supply connected between said electrode and said developing liquid whereby said developing liquid is atomized from said nozzle.

References Cited in the file of this patent UNITED STATES PATENTS 1,958,406 Darrah May 15, 1934 2,784,109 Walkup Mar. 5, 1957 2,940,847 Kaprelian June 14, 1960 3,001,888 Metcalfe et al Sept. 26, 1961 

1. THE METHOD OF DEVELOPING AN ELECTROSTATIC LATENT IMAGE BEARING MEMBER CAPABLE OF RETAINING ELECTROSTATIC CHARGES COMPRISING CONTACTING THE MEMBER WITH A BODY OF DIELECTRIC LIQUID, ELECTROSTATICALLY GENERATING WITHIN SAID DIELECTRIC LIQUID A SUPPLY OF FINELY DIVIDED DROPLETS OF A DEVELOPING LIQUID SUBSTANTIALLY IMMISCIBLE WITH SAID DIELECTRIC LIQUID, AND SELECTIVELY ELECTROSTATICALLY ATTRACTING SAID DROPLETS THROUGH SAID BODY OF LIQUID TO SAID LATENT IMAGE BEARING MEMBER IN ACCORDANCE WITH THE LATENT IMAGE THEREON. 